When a pair of gears mesh with each other, respective gear teeth engage with corresponding tooth spaces. Backlash is defined as the clearance between the gear teeth in a circumferential direction when the gears engage with each other. Backlash occurs when a pair of gears engage with each other, and one gear rotates in one direction and the other gear rotates in the opposite direction. The backlash occurs between the gears rotating in opposite directions. Built-in backlash is a tool for providing extra space between meshed teeth in an effort to overcome manufacturing errors. Excessive backlash causes unwanted chatter and vibration during operation.